The invention is generally directed to methods and apparatus for electronic reproduction of images. More specifically, the invention relates to a method and to an apparatus for the analysis of image originals for acquiring setting parameters for image setting in apparatus and systems for electronic image processing. What is to be understood herein by the term "image originals" are black-and-white original images and color original images.
Electronic image processing is essentially composed of the steps of image input, image processing and image output.
In the image input step, utilizing, for example, a color image scanner (scanner) as image input device, three primary color value signals (R, G, B) relating to the image original can be acquired. These signals generally are acquired with an optoelectronic scanner element on the basis of trichromatic as well as pixel-by-pixel and line-by-line scanning of the color image original to be reproduced, whereby the individual color value triads represent the color components "red" (R), "green" (G) and "blue" (B) in the color original. The analog color values are converted into digital color values and are stored for use in the following image processing step.
In the image processing step, the color values (R, G, B) are usually first converted into color separation values (C, M, Y, K) according to subtractive color mixing protocols, these being a measure for the dosing of the inks "cyan" (C), "magenta" (M), "yellow" (Y) and "black" (K) or, respectively, for the raster point sizes or raster percentages employed in the later printing process. Over and above this, various image parameters such as image light (or exposure) values and image depth values for an adaptation of the image scope, an image gradation characteristic for a correction of contrast or for a correction of overexposures and underexposures, as well as color cast values for a correction of color cast are set. Further, local and selective color corrections can also be undertaken, with the goal of improving the image reproduction, of compensating deficiencies or of undertaking editorial changes.
After the image processing step, the image output step is undertaken with a suitable image output device, for example a color separation printer or recorder for the rastered recording of color separations on a film material can be used.
The setting of the image parameters by an operator usually begins with the operator first pre-setting standard values that he identifies based on a rough pre-classification of the appertaining image original or based on an experienced guess. While setting the image parameters, the operator makes use of the measuring functions of the image input device in that he measures characteristic picture elements in the color original with the optoelectronic scanner element with respect to image scope, color cast and brightness distribution and uses the measured results for finding optimum setting values. The interpretation of the measured results and their conversion into optimum setting values for the image setting require a great deal of experience and often present difficulties for an unexperienced operator.
For parameterization of an image input device, it is already known to employ an automatic master analysis of the image original to be reproduced in view of image scope, image gradation and color casts and to use the results of the analysis for calculating image-dependent pre-setting values for setting the image parameters. Master analyses are known for image scope analyses, image gradation analyses and color cast analyses. The operator can then evaluate the result of the image analysis and transfer the offered pre-setting values directly into the device or modify or, respectively, correct them on the basis of measurement functions in order to undertake an optimum setting. As a result, the operator is relieved of routine jobs and can concentrate on the processing of color originals wherein global or selective color corrections are additionally required for improving the reproduction quality.
The known methods for master analysis are based on the color values (R, G, B) of the device-dependent RGB color space acquired from the respective image input device, whereby the analysis of the image scope and of the color cast is implemented with direct reference to the color values (R, G, B), whereas a brightness or luminance signal derived from the color values (R, G, B) is often employed for analysis of the image gradation.
The known methods for master analysis have the disadvantage that, given the connection of various image input devices, they must be specifically matched to the properties of the color values (R, G, B) of the respective image input devices.
The known methods for master analysis are also calculation-intensive, since the color values (R, G, B) acquired with the image input devices for the analysis must first be resolved into two color components and into a brightness component.